Reactive metal reagents are generally useful for reducing a variety of organic substrates, for example reducing ketones and aldehydes to olefins. See U.S. Pat. No. 4,225,734 to McMurry, which is incorporated by reference as if set forth at length herein for the details of such conversions. The McMurry '734 patent teaches reducing Ti(III) or Ti(IV) in the form of TiCl.sub.3 or TiCl.sub.4 to obtain the Ti.degree. active metal reagent. Suitable reducing agents are said to include alkali metals, for example sodium, potassium, or lithium. See the McMurry '734 patent at column 4, lines 21-24. Specific examples include LiAlH.sub.4 (Example II), LiBH.sub.4 (Example XIII), and K metal (Example XV).
The literature, however, acknowledges certain problems with the use of reduced metal catalysts as disclosed in the McMurry '734 reference. For example, some workers in the field reported difficulty in coupling saturated aliphatic ketones using Ti.degree. which had been reduced in the presence of LiAlH.sub.4. Reducing Ti.degree. via Rieke's method (K metal, TiCl.sub.3, in tetrahydrofuran (THF) solvent) was subsequently found to reliably convert both aliphatic and aromatic ketones to the corresponding symmetrical olefins. See McMurry, 41 J. Org. Chem. 896 (1976).
Further, the effectiveness of a particular combination of carbonyl feedstock and reducing agent has proven to be unpredictable. Low-valent titanium reagents (TiCl.sub.4 /Zn, TiCl.sub.3 /Mg, TiCl.sub.3 /LiAlH.sub.4) have been examined, and the results for the attempted dimerization of various aldehydes and ketones with the TiCl.sub.3 /LiAlH.sub.4 reagent are unpredictable, and have been described as "capricious". See McMurry, et al., 43 J. Org. Chem. 3255 (1978).
Moreover, the McMurry, et al. article notes that both the reaction of Li metal to the halide salt and the reduction of Ti(III) to Ti.degree. are incomplete, leaving residual reducing agent on the filter cake. See McMurry, et al. at page 3255, column 2, as well as the Experimental Section at page 3263 et seg. Particularly, the reference notes that the filter cake resulting from TiCl.sub.3 reduction with K metal is pyrophoric. Thus removing the reactive residual metal-containing reagents from the product mixture, particularly by means such as aqueous acid workup, has proven to be a major obstacle in purifying carbonyl reduction products. For example, in some cases, washing with acid, for example, cold 2N aqueous HCl, is the only practical and effective means for removing residual Li metal from the olefin product. Clearly, it would be desirable to avoid the potentially hazardous procedure of contacting a reactive metal with an aqueous acid.
The McMurry et al. article further notes that excess TiCl.sub.3 as well as excess reducing agent, i.e., LiAlH.sub.4, is required due to the characteristically incomplete reaction of the Ti halide salt and the reducing agent. Thus it would further be desirable to decrease reagent costs for carbonyl coupling reactions by employing substantially stoichiometric quantities of the metal compound and the reducing agent.